The engine immobiliser system is designed to prevent the vehicle from being stolen. This system uses a transponder key ecu that stores the key codes of authorized ignition keys. If an attempt is made to start the engine using an unauthorized key, the ecu sends a signal to the ecm to prohibit fuel delivery and ignition, effectively disabling the engine.

The transponder key coil receives this signal, the transponder key amplifier amplifies it, and then the signal is transmitted to the ecu. The ecu matches the key's id code with the vehicle's id code, which was previously registered in the ecu and then communicates the results to the ecm using sfi communication.
Engine immobiliser system
How to proceed with troubleshootingPrecaution
Precaution for vehicle with srs airbag and
seat belt pretensioner
Some operations in this section may affect the srs
airbags and seat belt pretensioner. Prior to
performing the corresponding operations, read the
srs airbag notice (see page rs-1).
Components
...
Removal
Disconnect cable from negative battery
terminal
Caution:
Wait at least 90 seconds after disconnecting the
cable from the negative (-) battery terminal to
prevent airbag and seat belt pretensioner activation.
Remove front seat track bracket outer
cover lh (see page se-11)
Remove fr ...
Dtc check / clear
Check dtc
Connect the intelligent tester to the dlc3.
Turn the ignition switch on and turn the tester on.
Select the following menu item: body / sliding roof /
dtc.
Check the dtc(s).
Clear dtc
Connect the intelligent tester to the dlc3.
Turn the ignition switch on ...